Method for forging a metallic workpiece

ABSTRACT

During the forging of a metallic workpiece (W) with at least four forging tools ( 1, 2 ) which are mutually opposite in pairs and are mutually angularly offset about the forging axis (S), the workpiece (W) is deformed under prevention of any lateral flow during each forging stroke by the deforming forging tools ( 1, 2 ) which enclose the workpiece cross section and is subjected to a hydrostatic pressure all over. In order to achieve in addition to the favorable dense forging due to the hydrostatic pressure Iall over a kneading effect for the desired improvement of the structure, the workpiece (W), prior to the final enclosure of the workpiece cross section and the consequent deformation obstructing the lateral flows is deformed during each forging stroke by an uneven deformation effect of the mutually angularly offset pairs of forging tools ( 1, 2 ) in addition with an at least reduced obstruction to lateral flow.

FIELD OF THE INVENTION

[0001] The invention relates to a method for forging a metallicworkpiece with at least four forging tools which are mutually oppositein pairs and are angularly offset against one another about the forgingaxis, according to which the workpiece is deformed under prevention ofany lateral flow during each forging stroke by the simultaneouslydeforming forging tools which enclose the workpiece cross section, andis subjected to a hydrostatic pressure all over.

DESCRIPTION OF THE PRIOR ART

[0002] The forging of a metallic workpiece, especially a continuouslycast workpiece, is to substantially close the blowholes and poresoccurring during the solidification of the molten metal and reduce theoccurring segregations on the one hand, and on the other hand to breakup the solidification structure with its coarse crystal structure andtransfer the same to a compact grained state, with the build-up of anall-over hydrostatic pressure being responsible for the compression andthus for the elimination of cavities and a consistent deformation withits destruction of the coarse crystal structure for a re-crystallizationand the dependent improvement of the structure.

[0003] The known forging methods can be principally broken down into thetwo-hammer and the four-hammer method, with the workpiece being forgedin the two-hammer method between two forging tools which deform relativeto one another and in the four-hammer method between at least foursimultaneously forging tools which are disposed mutually opposite inpairs and are mutually angularly offset about the forging axis.

[0004] According to the two-hammer method, an unobstructed lateral flowof the workpiece occurs during each forging stroke through the forgingtools which act only upon two mutually opposite sides of the workpiece,so that this material is strongly deformed and kneaded and only a lowhydrstatic pressure is allowed to build up. This two-hammer method leadstherefore to a very favorable improvement of the structure as a resultof the re-crystallization initiated with the deformation. However, arespective dense forging will only occur after several forging passesdue to lack of a higher hydrostatic pressure, i.e. only after largequality losses.

[0005] According to the four-hammer method, according to which the sameforging tools operate synchronously in the forging plane, the forgingtools enclose the workpiece during each forging stroke, thussubstantially preventing any lateral flow and the material deformationsubstantially leading to an elongation of the workpiece, so that due tothe weak kneading effect it also only possible to achieve a slightimprovement in the structure. Moreover, as a result of the deformationwhich occurs substantially in the longitudinal direction of theworkpiece, different mechanical properties of the material are obtainedin the longitudinal and lateral direction. Particularly the impact valuedecreases in the lateral direction. However, a high hydrostatic pressureis built up by the forging tools which enclose the workpiece crosssection all over, which ensures outstandingly dense forging.

SUMMARY OF THE INVENTION

[0006] The invention is therefore based on the object of providing amethod of the kind mentioned above which combines in a rational mannerthe advantages of the two-and four-hammer method and ensures during theforging of a workpiece both a desired improvement of the structure aswell as a sufficiently dense forging.

[0007] The invention achieves this object in such a way that theworkpiece, prior to the final enclosure of the workpiece cross sectionand the consequent deformation obstructing the lateral flow, is deformedduring each forging stroke by an uneven deformation effect of themutually angularly offset pairs of forging tools in addition with an atleast reduced obstruction to lateral flow.

[0008] Before the workpiece cross section is fully enclosed duringforging by the forging tools, it can be kneaded and fulled in aconcentrated manner within a suitable passage zone due to a respectiveuneven deformation effect of the mutually angularly offset pairs offorging tools, because in this passage zone the pairs of forging toolsdo not grasp and process the workpiece cross section in an even manner,but instead the one pair of forging tools advances in its working effectto the other pair(s) of forging tools and therefore there is only areduced obstruction to the lateral flow or no obstruction whatsoever.During each forging stroke there is an indepth deformation as aprecondition for the desired re-crystallization of the material. Thecomplete enclosure of the workpiece cross section by the forging toolsat the end of the forging stroke or in the zone of the end cross sectionof the forging tools also leads in each forging stroke to a highhydrostatic pressure which acts all over and ensures the respectivedense forging. Although the achievable level of the hydrostatic pressureremains lower than the one achieved during the conventional four-hammermethod, it is still sufficient to eliminate the cavities in theworkpiece which are caused by the casting. The omission of excessivehydrostatic pressure levels allows in contrast to the known four-hammermethod the structure-improving workpiece deformation with a lacking orlower obstruction to lateral flow. Relevant for the method is thereforethe combination of a deformation with an obstruction to lateral flow andhigh hydrostatic pressure build-up and a workpiece deformation withoutany stronger obstruction to lateral flow with an only lower hydrostaticpressure build-up. There can be different zones of said types ofdeformation in the pass-through direction depending on the workpiece andmaterial as a result of the forging tools. Merely the last zone duringthe exit of the material from the forging tools will preferably be azone with deformation obstructing lateral flow in order to enable thecalibration of the exiting workpiece.

[0009] In order to achieve the adjacency of deformations with strongeror lower obstruction to lateral flow, the forging tools can be providedwith respectively adjusted impact surface shapes and the movementsequences of the forging tools can be influenced in a suitable manner.It is understood that the two measures can also be combined with oneanother.

[0010] The uneven deformation effect of the mutually angularly offsetpairs of forging tools is achieved by using forging tools withdifferently shaped impact surfaces which converge into the same endcross section, however, as a result of which the one pair of tools withimpact surfaces which are bulged in comparison with the impact surfacesof the other pair of tools touches down at first on the workpiece duringsynchronous forging tool movements and can deform the material in thezone of said bulging with free lateral flow in the time until the latertouchdown of the other pair of tools. The end cross section of theimpact surfaces which is the same in all tools then finally not onlyleads to the build-up of a high hydrostatic pressure all over, but alsoto the calibration of the workpiece leaving the tools.

[0011] A further possibility of an uneven deformation effect is obtainedwhen the mutually angularly offset pairs of forging tools arestroke-moved with a different stroke height from the same lower deadcenter position, as a result of which there is an uneven immersion inthe workpiece despite the simultaneous deformation of the forging tools.The joint lower dead center position again produces the required highhydrostatic pressure and the desired workpiece calibration.

[0012] If the mutually angularly offset pairs of forging tools, whichcan also be provided with an identical arrangement, are subjected to adifferent stroke movement which can each be triggered per se, theunevenness of the deformation effect of said pairs of tools can bevaried within wide ranges and be adjusted to the respective forgingconditions.

BRIEF DESCRIPTION OF THE DRAWING

[0013] The subject matter of the invention is shown schematically in thedrawings, wherein:

[0014]FIG. 1.1 to FIG. 1.4 show the performance of the forging methodaccording to the invention on the basis of four tool positions duringthe forging stroke in a crosssectional view along line I-I in FIG. 3 and4;

[0015]FIG. 2.1 to FIG. 2.3 show a modified mode of operation accordingto this forging method on the basis of three tool positions in a forgingstroke also in a crosssectional view along line I-I in FIG. 3 and 4;

[0016]FIGS. 3 and 4 show axial sectional views along lines III-III andIV-IV of FIG. 1.4 and 2.3, respectively, and

[0017]FIG. 5 shows a cross-sectional view along line V-V of FIG. 3 andFIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] For the purpose of forging a metallic workpiece W with at leastfour forging tools 1, 2 which are mutually disposed opposite of oneanother in pairs and are mutually angularly offset about the forgingaxis S, the workpiece W is deformed by the forging tools 1, 2 enclosingthe workpiece cross section during each forging stroke by obstructinglateral flow and subjected to a hydrostatic pressure all over, so thatfavorable dense forging occurs. In order to also ensure a desiredimprovement in the structure, the workpiece W, prior to the finalenclosure of the workpiece cross section and the thus linked deformationthat prevents lateral flow, is additionally deformed during each forgingstroke by an uneven deformation effect of the mutually angularly offsetpairs of forging tools 1, 2 with at least a reduced obstruction tolateral flow.

[0019] For this purpose, as is indicated in FIGS. 1.1 to 1.4 forexample, pairs of forging tools 1, 2 with differently shaped impactsurfaces 3, 4 which converge into the same end cross section, however,as a result of which the one pair of tools 1 with its impact surfaces 3which are bulged as compared with the other pair of tools 2 touches downfirst on the workpiece W during synchronous forging tool movements andcan deform the material of the workpiece W in the zone 5 of said bulgingwith free lateral flow (FIG. 1.2, FIG. 1.3) in the time until the latertouchdown of the other pair of tools 2.

[0020] Another possibility of such an uneven deformation effect isobtained (as is indicated in FIGS. 2.1 to 2.3) when the mutuallyangularly offset pairs of forging tools 1, 2 are stroke-moved with adifferent stroke height (FIG. 2.1, FIG. 2.2) from the same lower deadcenter position (FIG. 2.3), as a result of which there is again anuneven immersion of the forging tools in the workpiece W. This methodwith different stroke height can be performed with forging tools 1, 2both of similarly and also differently arranged impact surfaces 3, 4.

[0021] The end of the forging stroke (FIG. 1.4, 2.3) then also leadsduring each forging stroke to a high hydrostatic pressure all over dueto the tools enclosing the workpiece cross section, which hydrostaticpressure ensures the respective dense forging. In the zone of the endcross section of the pairs of forging tools (FIG. 5)9 a zone 6 whichobstructs lateral flow and with calibrating deformation will be providedat the exit of the workpiece from the forging tools.

1. A method for forging a metallic workpiece with at least four forgingtools which are mutually opposite in pairs and are mutually angularlyoffset about the forging axis, according to which the workpiece isdeformed under prevention of any lateral flow during each forging strokeby the simultaneously deforming forging tools which enclose theworkpiece cross section and is subjected to a hydrostatic pressure allover, wherein the workpiece, prior to the final enclosure of theworkpiece cross section and the consequent deformation obstructing thelateral flow, is deformed during each forging stroke by an unevendeformation effect of the mutually angularly offset pairs of forgingtools in addition with an at least reduced obstruction to lateral flow.2. A method as claimed in claim 1, wherein the uneven deformation effectof the mutually angularly offset pairs of forging tools is achieved byusing forging tools with differently shaped impact surfaces whichconverge into the same end cross section,
 3. A method as claimed inclaim 1 or 2, wherein the mutually angularly offset pairs of forgingtools are stroke-moved with a different stroke height from the samelower dead center position.
 4. A method as claimed in claim 1 or 2,wherein the mutually angularly offset pairs of forging tools aresubjected to a different stroke movement which can each be triggered perse.